Methods and apparatus to control grayscale photolithography

ABSTRACT

Methods and apparatus to control grayscale lithography are disclosed. A disclosed example apparatus for adjusting a grayscale lithography process includes an optical measurement device to optically measure portions of a patterned wafer, and a processor to calculate a profile based on the measured portions, and to determine an adjustment of the grayscale lithography process based on the calculated profile. The disclosed apparatus also includes an adjuster to control the grayscale lithography process based on the adjustment.

FIELD OF THE DISCLOSURE

This disclosure relates generally to photolithography, and, moreparticularly, to methods and apparatus to control grayscalephotolithography.

BACKGROUND

In recent years semiconductor devices and microelectromechanical systemshave been fabricated with three-dimensional (3-D) features (e.g.,fabricated device features), such as inclined or ramped surfaces usinggrayscale photolithography. In such examples, the inclined surfaces maybe implemented as semiconductor or microelectromechanical devicefeatures and/or shapes. To produce such 3-D structures, the grayscalephotolithography controls a degree to which a resist layer is exposed toincident light energy. In some known examples, higher intensity exposureremoves an increased amount of the resist layer.

However, dimensional process control of inclined or ramped surfacesdefined by such processes can be difficult. Typically, measureddimensional or tolerance data to adjust the photolithographic process isnot obtained until after die and/or wafer fabrication is completed and,thus, is only available for post-production process adjustments.Further, known measuring techniques to measure features for controlpurposes can be both time and labor intensive. In particular, some knownmeasuring techniques include use of a profilometer, which can entailrelatively long cycle times.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrate inclined or ramped semiconductor ormicroelectromechanical structures that may be produced by the examplesdisclosed herein.

FIG. 2 is a schematic overview of an example grayscale photolithographyprocess adjustment system in accordance with the teachings of thisdisclosure.

FIG. 3A is an isometric view of an example grayscale photolithographypattern in accordance with the teachings of this disclosure that may beproduced and utilized by the example process adjustment system of FIG.2.

FIG. 3B depicts a produced inclined profile that is shown inrelationship to example pads of the photolithography pattern of FIG. 3A.

FIG. 3C is a graph depicting correlation of electrode depth that may beimplemented in the examples disclosed herein.

FIG. 4 is a graph depicting an example profile that may be calculated bythe examples disclosed herein.

FIG. 5 depicts example measurement data that may be utilized by theexamples disclosed herein to monitor a process.

FIG. 6 depicts an example wafer having multiple die in which theexamples disclosed herein may be implemented.

FIG. 7 illustrates example characterization across exposure dose thatmay be collected with the example wafer of FIG. 6.

FIG. 8 is an example grayscale photolithography process monitoringsystem that may be used to implement the examples disclosed herein.

FIG. 9 is a flowchart representative of machine readable instructionswhich may be executed to implement the example process monitoring systemof FIG. 9.

FIG. 10 is a block diagram of an example processing platform structuredto execute the instructions of FIG. 9 to implement the example processmonitoring system of FIG. 8.

The figures are not to scale. Instead, to clarify multiple layers andregions, the thickness of the layers may be enlarged in the drawings.Wherever possible, the same reference numbers will be used throughoutthe drawing(s) and accompanying written description to refer to the sameor like parts. As used in this patent, stating that any part (e.g., alayer, film, area) is in any way positioned on (e.g., positioned on,located on, disposed on, or formed on, etc.) another part, indicatesthat the referenced part is either in contact with the other part, orthat the referenced part is above the other part with one or moreintermediate part(s) located therebetween. Stating that any part is incontact with another part means that there is no intermediate partbetween the two parts.

DETAILED DESCRIPTION

Methods and apparatus to control grayscale photolithography aredisclosed. Some known semiconductor fabrication processes employ agrayscale photolithography process that varies the photoresist removaldepth at a sufficient resolution to define a three-dimensional (3-D)feature, such as an inclined or ramped feature (e.g., a rampedsemiconductor or microelectromechanical device feature). However,accurate control of producing such 3-D features can be difficult toachieve. In particular, process characterization of these knownlithography processes are typically done after fabrication of aproduction wafer containing numerous die instead of during fabrication.

The examples disclosed herein enable highly accurate in-line (e.g.,mid-process, mid-fabrication, etc.) control of grayscalephotolithography, thereby enabling significantly tighter dimensionalcontrol of fabricated 3-D features (e.g., ramped, inclined and/or curvedfeatures). As a result, the examples disclosed herein can enablerelatively narrow fabrication tolerances of semiconductor devices orstructures and, thus, can enable highly accurate dimensional control.Further, the examples disclosed herein can increase yields of fabricatedsemiconductor or microelectromechanical devices by enabling inlineautomated adjustments of photolithography processes. These adjustmentscan adapt the photolithography process for parameters including, but notlimited to variation in materials, thickness, light variation, reticlevariation and/or manufacturing tolerances, etc.

The examples disclosed herein utilize patterns (e.g., developedpatterns) that include grayscale pads (e.g., grayscale metrology pads)in some examples to accurately control a grayscale lithography process.In particular, these pads have different depths and can be defined onmultiple die of the wafer during a fabrication process of the wafer.

According to the examples disclosed herein, depths of the metrology padsare optically measured so that a profile of the grayscale process iscalculated to adjust the lithography process. In particular, numerousparameters of the grayscale process are monitored and adjusted for(e.g., inline control of the grayscale photolithography process) bytaking optical measurements of depths (e.g., measured removal depth) ofthe pads so that the aforementioned profile can be calculated. Theseparameters of the grayscale photolithography process can be adjusted toinclude optical mask characteristics or placement, reticle dimensionalvariances, material variances, light emission variances, batch-to-batchvariability, resist variance, etc. In some examples, a drift (e.g., adie-to-die drift, a wafer-to-wafer drift, a wafer batch drift, etc.) ofthe grayscale lithography process is calculated so that the drift can beadjusted accordingly with a calculated target profile.

As used herein, the term “profile” can refer to a function,relationship, multivariable relationship/fit, tabular relationship,curve and/or mathematical relationship that characterizes a behavior ofa process or variances associated with the process. As used herein, theterm “drift” can refer to a shift and/or movement of a characteristicbehavior or function over time. As used herein, the terms “pattern” or“grayscale photolithography pattern” can refer to a fabrication ofsloped or 3-D features created with sub-resolution reticle features. Asused herein, the terms “three-dimensional” and “3-D” in the context offabrication can refer to features having defined gradients orangular/ramped surfaces.

As used herein, the term “grayscale” or “GS” can refer to a process(e.g., a 3-D lithography process) and/or feature that encompassesgradients or angular/ramped surfaces in photoresist in contrast to a 2-Dlithography process that produces only vertical walls/structures (e.g.,a zero or full depth photoresist patterning process). As used herein,the terms “optical measurement” or “optically measuring” can refer to amethodology and/or process that is associated with measuring wavelengthsand/or a shift in wavelength of light reflected such as spectroscopicellipsometry or dual beam spectrometry from a surface, a feature and/ora component.

FIGS. 1A-1C illustrate inclined or ramped semiconductor structures bywhich the examples disclosed herein may be implemented to accuratelyproduce. Turning to FIG. 1A, an example fabricated structure 100includes fabricated electrodes 102 having ramped/sloped or angledportions (e.g., ramped or angled 3-D portions) 104. The examplefabricated structure 100 also includes fabricated springs 106. In thisexample, the electrodes 102 are fabricated onto or within a substrate(e.g., a substrate metal layer, a substrate layer, etc.) 108.

To define the electrode 102 and the corresponding sloped profile 104,the substrate 108 is first coated with a photoresist (e.g., a spacer)122 (shown in FIG. 1C), and then the resist is patterned with agrayscale photolithography process. The angled profile 104 is created bypartially exposing the photoresist. In particular, the electrode 102 isproduced by depositing metal over the angled profile 104, and,subsequently, the electrode metal is patterned through a separatephotolithography and metal etch process.

FIG. 1B depicts another fabricated structure 110, which is fabricated ontop of the fabricated structure 100 of FIG. 1A. The fabricated structure110, which is a micron-scale movable multi-segment mirror for a lightprojector die in this example, includes movable mirror elements 112(hereinafter 112 a, 112 b, 112 c, etc.). In this example, the mirrorelements 112 are each supported at their respective pivot points (e.g.,rotational points, etc.) 116. In this example, the mirror elements areeach moved by the electrodes 102 (e.g., to project an image and/orvideo) and the flat and angled portions 104 enable this movement basedon their geometry. In the view of FIG. 1B, the mirror element 112 c isdepicted as pivoted away from a default centered orientation (e.g., anon-rotated orientation, a non-zero angle orientation).

Turning to FIG. 1C, a cross-sectional representation of dimensionsassociated with fabricated structures produced by grayscalephotolithography process is shown. According to the illustrated view ofFIG. 1C, a fabricated structure 120 is shown. The fabricated structure120 includes the aforementioned photoresist layer 122 and a metalconductor layer 124 (e.g., the substrate 108). According to view of FIG.1C, a ramped profile 126 (e.g., the sloped profiled 104) is defined inthe resist layer 122 and includes both a respective angle 128 and adepth 130.

In contrast to the examples of FIGS. 1A-1C, the examples disclosed belowenable relatively tight controls of both the angle 128 and the depth 130by adjusting at least one photolithography parameter based on opticallymeasuring portions of developed resist patterns during fabrication ofmultiple die onto a wafer, for example. Accordingly, the examplesdisclosed below are able to produce highly accurate fabrication of 3-Dfeatures based on these adjustments.

FIG. 2 is an overview of an example grayscale photolithography processadjustment system 200 in accordance with the teachings of thisdisclosure. The process adjustment system 200 of the illustrated exampleis implemented to define an inclined profile onto a photoresist 201 withaccurate dimensional and tolerance control. The example processadjustment system 200 includes a process adjuster 202, a variableillumination source (e.g., an exposure dose source, an adjustableillumination source, etc.) 204 and an optical measurement device (e.g.,an optical thickness measurement device, a metrology measuring device, aspectral ellipsometer, double beam spectrometer, interferometer, etc.)206. In this particular example, the photolithography process adjustmentsystem 200 also includes an optical mask 208, which includes firsttransmittance reticles or windows (e.g., chrome features, chromereticles, windows with chrome or clear sub-resolution features, etc.)210, intermediate transmittance windows 212, and tertiary transmittancewindows 214, all of which are separated by respective pitch distances218.

To define a 3-D inclined or ramped feature onto the photoresist 201, thevariable illumination source 204 of the illustrated example provideslight and/or energy to the optical mask 208. In particular, light isemitted through the optical mask 208 to define the inclined profile ofthe photoresist 201. Accordingly, the pitch distances 218 control aresolution of the inclined profile and a significantly high resolutioncan define a ramped or curved profile. According to the illustratedexample, the variable illumination source 204 and the optical mask 208are also used to develop an exposed pattern in addition to the inclinedprofile. In some examples, and as will be described in connection withFIGS. 3A-3C below, the developed pattern includes multiple pads ofvarying respective depths that are defined by varying transmittancelevels of light from the variable illumination source 204 via theoptical mask 208.

To adjust processes associated with defining a depth of ramped and/orcurved profiles of the photoresist 201 and, as will be discussed indetail below in connection with FIGS. 3A-10, the optical measurementdevice 206 of the illustrated example optically measures portions (e.g.,depth and/or thickness of separate grayscale pads) of the aforementioneddeveloped patterns produced onto the photoresist 201, such as an examplegrayscale photoresist pattern 300 described below in connection withFIG. 3. In this example, the optical measurement device 206 measuresreflected light intensity or a change in light polarization across aspectrum to calculate a thickness of photoresist removed. Theaforementioned measurements may be made by spectroscopic ellipsometry ordual beam spectrometry. Accordingly, the optical measurements areprovided to the example process adjuster 202 so that the processadjuster 202 can adjust at least one parameter of the grayscalelithography process and/or the fabrication process.

In some examples, the process adjuster 202 adjusts a value and/ormagnitude of an exposure dose from the variable illumination source 204for more accurate control of a depth and/or dimensions associated with aramped profile. In some examples, the process adjuster 202 evaluates andadjusts for parameters associated with the optical mask 208 (e.g.,transmittance properties of the optical mask 208, the pitch distances218, etc.). Additionally or alternatively, the process adjuster 202evaluates and adjusts for properties (e.g., material variances,thickness ranges, unevenness, etc.) of the photoresist 201.

While the examples disclosed herein are shown in relationship tograyscale photolithography, the examples disclosed herein may be appliedto any photolithography, etching, and/or fabrication process thatgenerates 3-D structures (e.g., ramped, curved and/or inclined 3-Dstructures).

FIG. 3A is an isometric view illustrating the aforementioned examplegrayscale photoresist pattern 300 in accordance with the teachings ofthis disclosure that may be produced and utilized for processadjustments by the example process adjustment system 200 of FIG. 2. Theexample photoresist pattern 300 of FIG. 3A includes a first pad (e.g., arectangular or square pad) 302, which represents little or no exposureto light energy, and a second pad 304 with a corresponding exposedregion 306. In this example, the second pad 304 represents a photoresistsurface development rate. The photoresist pattern 300 also includes athird pad 310 with an exposed region 312, as well as a transition region316. The pad 310 is positioned adjacent the second pad 304 andrepresents a photoresist bulk development rate. In some examples, theexample grayscale photolithography pattern 300 also includes a fourthpad 320 with a full depth removal portion 322 and a correspondingtransition region 324. As can be seen in the illustrated view of FIG.3A, example transmittance percentage values are shown. However, thesetransmittance values are only examples and any appropriate values may beutilized, as appropriate, to an application.

In this example, each of the pads 302, 304, 310, 320 are approximately30 microns in width and height with depths between approximately 0.01 to0.5 microns. However, any appropriate dimensions or size scales may beused.

According to the illustrated example, depths of each of the pads 302,304, 310, 320 are optically measured to calculate or determine a profile(e.g., a characterization profile, a correlation profile, a processcontrol profile, etc.) that is used to adjust at least one parameterassociated with a respective grayscale photolithography process.

While the pads 302, 304, 310, 320 of the illustrated example are shownarranged in a linear pattern/arrangement and in close relative proximityto one another, the pads 302, 304, 310, 320 can be arranged in a squareor rectangular pattern, a triangular pattern (for examples with threepads), or placed on distinct regions (e.g., opposite ends, differentportions, separate portions, etc.) of a die. While the pads 302, 304,310, 320 are shown with a substantially rectangular overall shape, thepads 302, 304, 310, 320 may be any appropriate shape including, but notlimited, circular, polygonal, pentagonal, hexagonal, etc.

FIG. 3B depicts an inclined or ramped feature (e.g., an inclinedfabricated feature, a 3-D grayscale feature, a produced pattern, etc.)350 that is shown in relationship to the example pads 302, 304, 310 320of the photoresist pattern 300 of FIG. 3A to illustrate how respectivedepths of the pads 302, 304, 310 320 correspond to inclined features. Inparticular, the inclined feature 350 can be produced accuratelyaccording to the examples disclosed herein. The inclined feature 350includes a respective depth 352 with a respective angle (e.g., anincline angle) 354. The inclined feature 350 also includes an uppersurface 356 that corresponds to the first pad 302, an incline 360 thatcorresponds to the pad 310 and the pad 304, and a region 364 thatcorresponds to the pad 320.

FIG. 3C is a graph 370 depicting correlation of electrode depth that maybe implemented in the examples disclosed herein. The example graph 370includes a vertical axis 372 that represents an electrode depth inangstrom (A) and a horizontal axis 374 that represents removal depth inangstrom. As can be seen in the illustrated example data points 376 areused to fit a line 378 (e.g., the line 378 if fit using linearregression.

FIG. 4 is a graph 400 depicting an example profile 401 that may becalculated or determined by the examples disclosed herein. Inparticular, the example profile 401 illustrates a relationship betweenoptically measured depths of the pads 302, 304, 310 described above inconnection with FIG. 3 with optical transmittance levels and/or exposuredoses. The graph 400 of FIG. 4 includes a vertical axis 402 thatrepresents resist thickness in nanometers (nm) and horizontal axis 404that represents exposure dose in Joules per meter squared (J/m²).

According to the illustrated example of FIG. 4, the profile 401 includesa full thickness portion 406 corresponding to the pad 302, and a surfacedevelop rate portion 408 that corresponds to differences between depthsof the pad 302 and the pad 304. Further, the example profile 401includes a bulk develop rate portion 410 that exhibits a linear slopedline representing differences between the pad 304 and the pad 310 (e.g.,a linear relationship). Further, the example profile 401 includes acomplete resist removal portion 412.

To calculate the example profile 401, depths of the pads 304, 310, 320in relation to a reference full thickness photoresist or unexposedregion of the pad 302 are utilized to define the sloped line thatencompasses the bulk develop rate portion 410. Additionally oralternatively, the surface develop rate portion 408 is used to define aninitial start of the bulk develop rate portion 410. In some examples,the sloped line is calculated by finding points of the profile 401 wherethe bulk develop rate portion 410 intersects both the surface developrate portion 408 and the complete resist removal portion 412.

FIG. 5 depicts example measurement data that may be utilized by theexamples disclosed herein to monitor a process using multiple profilesto characterize a grayscale photolithography process over exposure. Inparticular, a first graph 502 and a second graph 504 illustrate how theexamples disclosed herein may be used to monitor and control a 3-Dfabrication grayscale photolithography process amongst multipledeveloped patterns of different respective fabricated devices.

According to the illustrated example, both the first graph 502 and thesecond graph 504 include respective horizontal axes 506 that representexposure levels and a vertical axis 508 that represents resistthickness. In this example, a legend 510 represents opticaltransmittance percentages. Further, the graphs 502, 504 include a lowercontrol band 514 and an upper control band 516, both of which are usedto validate measured profiles of multiple grayscale patterns thatindicate deviation(s) from desired dimensional control of 3-D features.

In some examples, the lower control band 514 and the upper control band516 are used to determine an error of a reticle of an optical mask.Additionally or alternatively, a determination of photoresistbatch-to-batch consistency is monitored and/or calculated based onchanges or shifts of the first graph 502 or the second graph 504relative to the lower control band 514 or the upper control band 516.

FIG. 6 illustrates an example wafer 602 having multiple die 603 in whichthe examples disclosed herein may be implemented. In this example, padlocations 604 are shown relative to the corresponding die 603. Inparticular, the pad locations 604 are provided with the developedgrayscale pattern 300 with the pads 302, 304, 310, each of which are tobe optically measured to calculate a profile, such as the profile 401 ofFIG. 4. In turn, the calculated profile is monitored for changes and/ordeviations from a specification (e.g., threshold bands or tolerances ofthe specification). In this example, pairs of “top” and “bottom” die aremonitored in conjunction with one another.

FIG. 7 illustrates example monitoring that may be implemented with theexample wafer 602 of FIG. 6. According to the illustrated example ofFIG. 7, graphs 702 represent “top” die of the wafer 602 while graphs 704represent “bottom” die of the wafer 602. As a result, shifts orirregularities between the “bottom” die as well as the top “die” aremonitored, thereby enabling consistent and effective determination ofvariation related to optical masks and/or their corresponding reticlefeature consistency. In some examples, “top” and “bottom” pairs arecompared to other “top” and “bottom” pairs to adjust and/or control agrayscale lithography process. Additionally, multiple sets ofmeasurement pads on the same reticle can be used to evaluate exposuresystem uniformity.

FIG. 8 illustrates an example photolithography process monitoring system800 that may be used to implement the examples disclosed herein. Inparticular, the process monitoring system 800 may be implemented in theprocess adjuster 202 shown in FIG. 2. The process monitoring system 800of the illustrated example includes a grayscale lithography processanalyzer 802 including an optical thickness measurement analyzer 804, adrift analyzer 806, and a process adjustment calculator 808. Further,the example process monitoring system 800 includes a light sourceexposure controller 810 that is communicatively coupled to the exampleprocess adjustment calculator 808 via a communication line 812.

To characterize a grayscale lithography process, the optical thicknessmeasurement analyzer 804 of the illustrated example utilizesmeasurements made by the optical measurement device 206. In thisexample, the optical measurement device 206 optically measures portionsof the developed photoresist pattern 300 to calculate a profile (e.g.,the profile 401). In particular, the corresponding depths of the firstpad 302, the second pad 304 and the third pad 310 are optically measuredbased on spectral ellipsometry or reflectance spectrometry to calculatethe profile. In other examples, optical measurements of the fourth pad320 are also used to calculate the profile. In some examples, theexample optical thickness measurement analyzer 804 determines a surfacedevelop rate and a bulk develop rate, both of which may be characterizedas relatively straight lines (e.g., fitted lines, regression definedlines, etc.) having corresponding slopes. In some examples, the profileis calculated to adjust exposure of a resist. Additionally oralternatively, the profile is calculated to evaluate an optical mask ora reticle. In other examples, the profile is calculated to evaluateresist material and/or batches of resist material. In some examples,prior material measurements and/or associated data are provided to theoptical thickness optical thickness measurement analyzer 804.

To determine an adjustment of the grayscale lithography process, theexample process adjustment calculator 808 utilizes the aforementionedcalculated profile to determine how to adjust the grayscale lithographyprocess. For example, the process adjustment calculator 808 cancalculate a change in exposure dose by the variable illumination source204 to more accurately control resist removal depth (e.g., a slope of abulk develop rate) of the grayscale lithography process. In someexamples, the optical mask 208 is rejected or redesigned to pattern thecorrect profile for a given exposure dose.

To adjust the grayscale lithography process, the process adjustmentcalculator 808 and/or the photolithography exposure controller 812 causean adjustment of the grayscale lithography process based on thedetermined adjustment by the example process adjustment calculator 808.In this example, the process adjustment calculator 808 directs theprocess adjuster 202 and/or the light source exposure controller 810 tovary incident light exposure dose.

In some examples, the drift analyzer 806 determines a potential drift ofthe grayscale lithography process. For example, the drift analyzer 806can determine that depth removal using the optical mask 208 is shiftingbased on multiple resist batches and/or drifting related to the opticalmask 208. As a result, the drift analyzer 806 may cause furtheradjustments of the grayscale lithography process by the processadjustment calculator 808 and/or the light source exposure controller810. In some examples, measurements of the first pad 302, the second pad304 and the third pad 310 are used to determine production batch shiftsand/or reworks (e.g., stripping of a resist for later re-application,etc.). Additionally or alternatively, the measurements are used todetermine batch-to-batch adjustments of the grayscale lithographyprocess. In other words, the examples disclosed herein may be used toshift the grayscale lithography process.

While an example manner of implementing the grayscale photolithographyprocess adjustment system 200 of FIG. 2 is illustrated in FIG. 8, one ormore of the elements, processes and/or devices illustrated in FIG. 8 maybe combined, divided, re-arranged, omitted, eliminated and/orimplemented in any other way. Further, the example optical thicknessmeasurement analyzer 804, the example drift analyzer 806, the exampleprocess adjustment calculator 808, the example light source exposurecontroller 810 and/or, more generally, the example process monitoringsystem 800 of FIG. 8 may be implemented by hardware, software, firmwareand/or any combination of hardware, software and/or firmware. Thus, forexample, any of the example optical thickness measurement analyzer 804,the example drift analyzer 806, the example process adjustmentcalculator 808, the light source exposure controller 810 and/or, moregenerally, the example process monitoring system 800 could beimplemented by one or more analog or digital circuit(s), logic circuits,programmable processor(s), application specific integrated circuit(s)(ASIC(s)), programmable logic device(s) (PLD(s)) and/or fieldprogrammable logic device(s) (FPLD(s)). When reading any of theapparatus or system claims of this patent to cover a purely softwareand/or firmware implementation, at least one of the example, opticalthickness measurement analyzer 804, the example drift analyzer 806, theexample process adjustment calculator 808 and/or the example lightsource exposure controller 810 is/are hereby expressly defined toinclude a non-transitory computer readable storage device or storagedisk such as a memory, a digital versatile disk (DVD), a compact disk(CD), a Blu-ray disk, etc. including the software and/or firmware.Further still, the example photolithography process monitoring system800 of FIG. 8 may include one or more elements, processes and/or devicesin addition to, or instead of, those illustrated in FIG. 8, and/or mayinclude more than one of any or all of the illustrated elements,processes and devices.

A flowchart representative of example machine readable instructions forimplementing the process adjustment system 200 of FIG. 2 is shown inFIG. 9. In this example, the machine readable instructions comprise aprogram for execution by a processor such as the processor 1012 shown inthe example processor platform 1000 discussed below in connection withFIG. 10. The program may be embodied in software stored on anon-transitory computer readable storage medium such as a CD-ROM, afloppy disk, a hard drive, a digital versatile disk (DVD), a Blu-raydisk, or a memory associated with the processor 1012, but the entireprogram and/or parts thereof could alternatively be executed by a deviceother than the processor 1012 and/or embodied in firmware or dedicatedhardware. Further, although the example program is described withreference to the flowchart illustrated in FIG. 9, many other methods ofimplementing the example grayscale lithography process adjustment system200 may alternatively be used. For example, the order of execution ofthe blocks may be changed, and/or some of the blocks described may bechanged, eliminated, or combined. Additionally or alternatively, any orall of the blocks may be implemented by one or more hardware circuits(e.g., discrete and/or integrated analog and/or digital circuitry, aField Programmable Gate Array (FPGA), an Application Specific Integratedcircuit (ASIC), a comparator, an operational-amplifier (op-amp), a logiccircuit, etc.) structured to perform the corresponding operation withoutexecuting software or firmware.

As mentioned above, the example processes of FIG. 9 may be implementedusing coded instructions (e.g., computer and/or machine readableinstructions) stored on a non-transitory computer and/or machinereadable medium such as a hard disk drive, a flash memory, a read-onlymemory, a compact disk, a digital versatile disk, a cache, arandom-access memory and/or any other storage device or storage disk inwhich information is stored for any duration (e.g., for extended timeperiods, permanently, for brief instances, for temporarily buffering,and/or for caching of the information). As used herein, the termnon-transitory computer readable medium is expressly defined to includeany type of computer readable storage device and/or storage disk and toexclude propagating signals and to exclude transmission media.“Including” and “comprising” (and all forms and tenses thereof) are usedherein to be open ended terms. Thus, whenever a claim lists anythingfollowing any form of “include” or “comprise” (e.g., comprises,includes, comprising, including, etc.), it is to be understood thatadditional elements, terms, etc. may be present without falling outsidethe scope of the corresponding claim. As used herein, when the phrase“at least” is used as the transition term in a preamble of a claim, itis open-ended in the same manner as the term “comprising” and“including” are open ended.

The program of FIG. 9 begins as photoresist pattern 300 and the feature350 are defined on a wafer (e.g., a die of the wafer) by a grayscalephotolithography process, for example (block 902). In particular thepattern 300 includes, pads, such as the pads 302, 304, 310, all of whichare defined onto a portion of the die in a relatively linear arrangementin this example.

According to the illustrated example, the optical measurement device 206optically measures portions (e.g., pads) of the developed photoresistpattern 300 (block 904). In particular, the optical measurement device206 measures depths of each of the pads 302, 304, 310 based on reflectedwavelengths from the pads 302, 304, 310.

Next, the optical thickness measurement analyzer 804 of the illustratedexample calculates a profile of the inclined feature 350 based on themeasurements of the grayscale metrology pads (block 906). In thisexample, the optical thickness measurement analyzer 804 generates curves(e.g., linear curves) based on the measured depths of each of the pads302, 304, 310. In some examples, a depth of the pad 320 is alsomeasured.

According to the illustrated example, the process adjustment calculator808 directs the process adjuster 202 and/or the light source exposurecontroller 810 to adjust the light exposure process (block 907). In thisexample, thickness/depth measurement errors are used to adjust a laterproduction lot's exposure dose/level. Additionally or alternatively, theexample process adjuster 202 adjusts a parameter such as exposurerelated to an optical mask, exposure tool's characteristics, and/ormaterial batch selection, etc.

It is then determined whether the profile and/or a drift associated withthe profile is within tolerances (e.g., error bands, tolerance bands,etc.) (block 908). If it is determined that the profile and/or the driftassociated with the profile is not within tolerances (block 908),control of the process proceeds to block 911. Otherwise, the processends.

In some examples, a production lot and/or a photoresist layer isreworked (block 911). In particular, an entire production lot ofmaterial, for example, may be reworked by stripping the photoresistlayer. In some examples, a photoresist of a partially produced wafer,for example, may be stripped for re-application of the photoresist.Control of the process then returns to block 902.

FIG. 10 is a block diagram of an example processor platform 1000 capableof executing the instructions of FIG. 9 to implement the processadjustment system 200 of FIG. 2. The processor platform 1000 can be, forexample, a server, a personal computer, or any other type of computingdevice.

The processor platform 1000 of the illustrated example includes aprocessor 1012. The processor 1012 of the illustrated example ishardware. For example, the processor 1012 can be implemented by one ormore integrated circuits, logic circuits, microprocessors or controllersfrom any desired family or manufacturer. The hardware processor may be asemiconductor based (e.g., silicon based) device. In this example, theprocessor 1012 implements the example optical measurement analyzer 804,the example drift analyzer 806, the process adjustment calculator 808and the example light source exposure controller 810.

The processor 1012 of the illustrated example includes a local memory1013 (e.g., a cache). The processor 1012 of the illustrated example isin communication with a main memory including a volatile memory 1014 anda non-volatile memory 1016 via a bus 1018. The volatile memory 1014 maybe implemented by Synchronous Dynamic Random Access Memory (SDRAM),Dynamic Random Access Memory (DRAM), RAMBUS Dynamic Random Access Memory(RDRAM) and/or any other type of random access memory device. Thenon-volatile memory 1016 may be implemented by flash memory and/or anyother desired type of memory device. Access to the main memory 1014,1016 is controlled by a memory controller.

The processor platform 1000 of the illustrated example also includes aninterface circuit 1020. The interface circuit 1020 may be implemented byany type of interface standard, such as an Ethernet interface, auniversal serial bus (USB), and/or a PCI express interface.

In the illustrated example, one or more input devices 1022 are connectedto the interface circuit 1020. The input device(s) 1022 permit(s) a userto enter data and/or commands into the processor 1012. The inputdevice(s) can be implemented by, for example, an audio sensor, amicrophone, a camera (still or video), a keyboard, a button, a mouse, atouchscreen, a track-pad, a trackball, isopoint and/or a voicerecognition system.

One or more output devices 1024 are also connected to the interfacecircuit 1020 of the illustrated example. The output devices 1024 can beimplemented, for example, by display devices (e.g., a light emittingdiode (LED), an organic light emitting diode (OLED), a liquid crystaldisplay, a cathode ray tube display (CRT), a touchscreen, a tactileoutput device, a printer and/or speakers). The interface circuit 1020 ofthe illustrated example, thus, typically includes a graphics drivercard, a graphics driver chip and/or a graphics driver processor.

The interface circuit 1020 of the illustrated example also includes acommunication device such as a transmitter, a receiver, a transceiver, amodem and/or network interface card to facilitate exchange of data withexternal machines (e.g., computing devices of any kind) via a network1026 (e.g., an Ethernet connection, a digital subscriber line (DSL), atelephone line, coaxial cable, a cellular telephone system, etc.).

The processor platform 1000 of the illustrated example also includes oneor more mass storage devices 1028 for storing software and/or data.Examples of such mass storage devices 1028 include floppy disk drives,hard drive disks, compact disk drives, Blu-ray disk drives, RAIDsystems, and digital versatile disk (DVD) drives.

The coded instructions 1032 of FIG. 9 may be stored in the mass storagedevice 1028, in the volatile memory 1014, in the non-volatile memory1016, and/or on a removable tangible computer readable storage mediumsuch as a CD or DVD.

From the foregoing, it will be appreciated that example methods,apparatus and articles of manufacture have been disclosed that enableaccurate control of grayscale photolithography processes. The examplesdisclosed also enable inline control of semiconductor ormicroelectromechanical process that involve 3-D structures byfacilitating adjustments during fabrication of a wafer and/or a die.

Although certain example methods, apparatus and articles of manufacturehave been disclosed herein, the scope of coverage of this patent is notlimited thereto. On the contrary, this patent covers all methods,apparatus and articles of manufacture fairly falling within the scope ofthe claims of this patent. While the examples disclosed herein are shownin the context of grayscale photolithography, the example disclosedherein may be applied to any appropriate lithography, etching and/orfabrication process that transfers a photoresist grayscale profile intoan underlying substrate (e.g., chemical etching, dry plasma etching,mechanical etching, etc.).

What is claimed is:
 1. An apparatus for adjusting a grayscalelithography process, the apparatus comprising: an optical measurementdevice configured to optically measure a plurality of patterns of apatterned wafer, each pattern being associated on a one-to-one basiswith a corresponding different die on the wafer and each patternincluding a plurality of locations each having a different thickness ofdeveloped photoresist, a processor to: calculate a profile based on themeasured locations, and determine an adjustment of the grayscalelithography process based on the calculated profile; and an adjuster tocontrol the grayscale lithography process based on the adjustment. 2.The apparatus as defined in claim 1, wherein a developed pattern of thepatterned wafer includes pads of varying respective depths.
 3. Theapparatus as defined in claim 2, wherein the developed pattern isdefined by an adjustable illumination source onto the patterned wafervia an optical mask.
 4. The apparatus as defined in claim 3, wherein theoptical mask includes windows with at least one of opaque, chrome orclear sub-resolution features to locally modulate a transmittance of anexposure.
 5. The apparatus as defined in claim 2, the processor is tocalculate the profile based on optical measurements of the respectivedepths of the pads.
 6. The apparatus as defined in claim 2, wherein thepads are sufficiently sized to be optically measured.
 7. The apparatusas defined in claim 6, wherein the pads are arranged as an array on thepatterned wafer.
 8. The apparatus as defined in claim 1, wherein theprofile includes a relationship pertaining to at least one of a bulkdevelop rate or a surface develop rate.
 9. The apparatus as defined inclaim 1, wherein the processor is to further calculate a drift of thegrayscale lithography process.
 10. The apparatus as defined in claim 1,wherein the pattern is defined in photoresist or the pattern is definedin photoresist and transferred to an underlying substrate via a chemicalor dry plasma etching process.
 11. The apparatus as defined in claim 1,wherein the plurality of patterns is a plurality of first patterns, andthe optical measurement device is further configured to opticallymeasure a plurality of second patterns of the patterned wafer, eachsecond pattern being located on a same die as a corresponding one of thefirst patterns.
 12. The apparatus as defined in claim 11, wherein theoptical measurement device is further configure to determine adifference between first and second patterns on a same die.
 13. A methodfor process control of a grayscale lithography process, the methodcomprising: defining a developed pattern on a wafer by varyingtransmittance of an exposure source to define a plurality of patterns ofa patterned wafer, each pattern being associated on a one-to-one basiswith a corresponding different die on the wafer and each patternincluding a plurality of locations each having a different thickness ofdeveloped photoresist; optically measuring, via an optical thicknessmeasurement device, features of the patterns; calculating, via aprocessor, a profile of the grayscale lithography process based onmeasuring the features; and adjusting an exposure of the wafer based onthe profile.
 14. The method as defined in claim 13, further includingcalculating a drift of the grayscale lithography process based on ameasured removal depth of the developed pattern and calculated profile.15. The method as defined in claim 13, wherein the defining thedeveloped pattern includes defining pads of differing respective depths.16. The method as defined in claim 15, wherein the calculating theprofile is at least partially based on the respective depths of thepads.
 17. The method as defined in claim 13, wherein the developedpattern is defined by a lithography process, or by transferring apattern in photoresist to an underlying substrate via a chemical or dryplasma etching process.
 18. The method as defined in claim 13, whereinthe plurality of patterns is a plurality of first patterns, and definingthe developed pattern includes varying transmittance of the exposuresource to define a plurality of second patterns, each second patternbeing located on a same die as a corresponding one of the firstpatterns, further comprising the optical measurement device opticallymeasuring, via the optical thickness measurement device, features of thesecond patterns, and calculating the profile of the grayscalelithography process is also based on measuring the features of thesecond patterns.
 19. The apparatus as defined in claim 18, whereincalculating the profile includes determining a difference between firstand second patterns on a same die.
 20. A tangible non-transitory machinereadable medium comprising instructions, which when executed, cause aprocessor to at least: calculate a profile of each of a plurality ofpatterns on a wafer based on optical thickness measurements of aplurality of locations within each of the patterns, each of the patternsbeing associated on a one-to-one basis with a different correspondingdie on the wafer, and each of the locations having a different thicknessof developed photoresist; determine an adjustment of a grayscalelithography process based on the profile; and adjust the grayscalelithography process based on the determined adjustment.
 21. The tangiblemachine readable medium as defined in claim 20, wherein the pads havedifferent respective depths.
 22. The tangible machine readable medium asdefined in claim 20, wherein the profile includes a linear linecorresponding to the pattern that is based on at least one of a surfacedevelop rate and a bulk develop rate.
 23. The tangible machine readablemedium as defined in claim 20, wherein the instructions cause theprocessor to determine a drift of the grayscale lithography process. 24.The tangible machine readable medium as defined in claim 20, wherein theinstructions cause the processor to adjust the grayscale lithographyprocess during fabrication of semiconductor or microelectromechanicaldevices on the wafer.
 25. The tangible machine readable medium asdefined in claim 20, wherein the plurality of patterns is a plurality offirst patterns, and the instructions, when executed, further configurethe processor to calculate a profile of each of a plurality of secondpatterns on the wafer based on optical thickness measurements of aplurality of locations within each of the second patterns, each secondpattern being located on a same die as a corresponding one of the firstpatterns.
 26. The tangible machine readable medium as defined in claim25, wherein calculating the profile includes determining a differencebetween first and second patterns on a same die.